Smectite to illite transformation of Gulf of Mexico -Eugene Island (GoM-EI) mudrock

Abstract

Predicting pore pressure is an important job in the petroleum industry. Standard methods for estimating pressure do not apply to the basin where overpressure is often observed. Compaction disequilibrium and clay mineral diagenesis are recognized as potential contributors to overpressure generation. My research aims to look at the relationship between smectite-to-illite transformation and overpressure generation. The proposed research has two phases. Phase one objective is to study the reaction rate and the conditions such as temperature, time, KCl concentration that induce smectite-to-illite transformation. Phase two study objective is to investigate the change in compressibility and permeability of resedimented GoM-EI mudrock due to smectite-to-illite transformation. This thesis presents the results of phase one study. In phase one study, we have successfully transformed smectite to illite in laboratory environment using GoM-EL as starting material. Based on mineral composition results of cooked samples, it is clearly that illitization goes through three stages. The first stage is that a highly smectitic clay is represented by randomly ordered illite-smectite mixed layer phase (I/S). With increasing reaction, randomly ordered I/S are transformed into regularly interstratified structures. The third stage is that the ordered I/S reacts to a final discrete illite. Additional thermal gravimetric analysis (TGA) study on cooked samples confirms that the transformation is releasing water. However, we are unable to determine the volume change of the sample using mineral study.